Retrievable milling guide anchor apparatus and associated methods

Abstract

In a parent wellbore casing, full bore access to the portion of the casing beneath a lateral bore liner portion therein is provided using a specially designed tubular retrievable anchor assembly hydraulically set within the casing above the liner portion and having a depending mill guide portion. A milling pipe with a first rotary mill is extended through the anchor assembly, with the mill being laterally deflected by the guide to mill a partial opening through the bottom side wall of the liner portion. The milling pipe is then withdrawn from the casing, the first mill replaced with a second rotary mill, and a specially designed tubular retrieval collet coaxially secured to the milling pipe. The milling pipe is then extended downwardly through the anchor assembly, the second mill used to enlarge the initial liner opening, and the collet snapped into the anchor assembly. The anchor assembly is then retrieved by pulling up on the milling pipe to release the anchor assembly which is removed from the casing. A full bore mill, having an elongated nose portion guidingly receivable in the partial liner hole, is then lowered into the casing and used to bore out the liner portion within the casing to provide full bore access to the parent casing portion beneath the previous location of the lateral bore liner portion therein.

What is claimed is: 
     
       1. A tubular anchor assembly coaxially and releasably securable in a subterranean well bore casing, comprising: a tubular inner mandrel;   a tubular slip carrier coaxially circumscribing the inner mandrel in a radially outwardly spaced relationship therewith, the slip carrier having a circumferentially spaced series of side wall slip windows therein and outwardly bounding an annular space between the inner mandrel and the slip carrier;   a circumferentially spaced series of slips carried in the annular space for radial movement through the slip windows between retracted and extended positions; and   a circumferentially spaced series of arcuate, elongated spring members disposed in the annular space and resiliently biasing the slips toward their retracted positions, the spring members being interdigitated with the slips and having longitudinally central portions secured to the slip carrier, with each slip being engaged by end portions of two spring members on circumferentially opposite sides thereof.   
     
     
       2. The tubular anchor assembly of claim 1 wherein: the spring members are concavely curved toward the inner mandrel.   
     
     
       3. The tubular anchor assembly of claim 2 wherein: the slips have radially outer sides with recesses formed therein, and   the end portions of the spring members extend into the recesses.   
     
     
       4. The tubular anchor assembly of claim 3 wherein: the inner mandrel has an outer side surface in which a circumferentially spaced series of axially elongated pockets are formed,   the slips are slidably received in the pockets for movement along their lengths, and   the end portions of the spring members slidably engage the slips.   
     
     
       5. The tubular anchor assembly of claim 1 wherein: the tubular anchor assembly has an end portion adapted for connection to an end portion of an elongated mill guide member.   
     
     
       6. The tubular anchor assembly of claim 1 wherein: the tubular anchor assembly has a lower end portion adapted for connection to an upper end portion of an elongated mill guide member.   
     
     
       7. The tubular anchor assembly of claim 6 wherein: the upper end portion of the elongated mill guide member has an annular configuration with a circumferentially spaced series of axially extending tooth portions formed on its upper end, and   the lower end portion of the anchor assembly includes a circumferentially spaced series of axial notches formed on the lower end of the inner mandrel and adapted to be interlocked with the mill guide member tooth portions, and a tubular coupling member threadable onto the interlocked portions of the inner mandrel and mill guide member.   
     
     
       8. A tubular anchor assembly coaxially and releasably securable in a subterranean well bore casing, comprising: a tubular inner mandrel having an outer side surface in which a circumferentially spaced series of elongated axially extending pockets are formed;   a tubular slip carrier coaxially circumscribing the inner mandrel in a radially outwardly spaced relationship therewith, the slip carrier having a circumferentially spaced series of side wall slip windows therein and outwardly bounding an annular space between the inner mandrel and the slip carrier;   a circumferentially spaced series of slips disposed in the annular space, with radially outer portions of the slips being received in the slip windows for movement therethrough between radially retracted and radially extended positions, and radially inner portions received in the pockets for sliding movement along their lengths;   a biasing structure operative to resilient bias the slips to their radially retracted positions; and   a setting structure operative to force the slips from their radially retracted positions to their radially extended positions.   
     
     
       9. The tubular anchor assembly of claim 8 wherein the setting structure includes: a tubular wedge member coaxially and slidably circumscribing the inner mandrel, the wedge member having a circumferentially spaced series of sidewall slots extending axially inwardly through an end thereof and defining a circumferentially spaced series of collet finger portions of the tubular wedge member, the collet finger portions having outer ends that axially oppose end portions of the slips and are rampingly engageable therewith to drive the slips from their radially retracted positions to their radially extended positions.   
     
     
       10. The tubular anchor assembly of claim 9 wherein: the inner mandrel, the slips, and the wedge member are relatively movable in axial directions between (1) a set position in which the outer ends of the collet finger portions outwardly overlie and are radially supported by nonpocketed areas of the inner mandrel, and rampingly engage the end portions of the slips, and (2) a release position in which the outer ends of the collet finger portions overlie the inner mandrel pockets and may be radially deflected thereinto in response to an axially directed engagement force between the outer ends of the collet finger portions and the end portions of the slips.   
     
     
       11. The tubular anchor assembly of claim 8 wherein: the tubular anchor assembly has an end portion adapted for connection to an end portion of an elongated mill guide member.   
     
     
       12. The tubular anchor assembly of claim 8 wherein: the tubular anchor assembly has a lower end portion adapted for connection to an upper end portion of an elongated mill guide member.   
     
     
       13. The tubular anchor assembly of claim 12 wherein: the upper end portion of the elongated mill guide member has an annular configuration with a circumferentially spaced series of axially extending tooth portions formed on its upper end, and   the lower end portion of the anchor assembly includes a circumferentially spaced series of axial notches formed on the lower end of the inner mandrel and adapted to be interlocked with the mill guide member tooth portions, and a tubular coupling member threadable onto the interlocked portions of the inner mandrel and mill guide member.   
     
     
       14. A tubular anchor assembly coaxially and releasably securable in a subterranean well bore casing, comprising: a tubular inner mandrel having an outer side surface in which axially separated first and second circumferentially spaced series of elongated axially extending pockets are formed;   a tubular first slip carrier coaxially circumscribing the inner mandrel in a radially outwardly spaced relationship therewith, the first slip carrier having a circumferentially spaced series of first side wall slip windows therein that overlie the first series of pockets;   a tubular second slip carrier coaxially circumscribing the inner mandrel in a radially outwardly spaced relationship therewith, the second slip carrier having a circumferentially spaced series of second side wall slip windows therein that overlie the second series of pockets;   a circumferentially spaced series of first slips carried between the inner mandrel and the first slip carrier, the first slips having radially inner portions carried in the first series of pockets for sliding movement along their lengths, radially outer portions received in the first side wall slip windows for movement therethrough between radially retracted and radially extended positions, and tapered ends;   a circumferentially spaced series of second slips carried between the inner mandrel and the second slip carrier in an axially spaced, opposing relationship with the first slips, the second slips having radially inner portions carried in the second series of pockets for sliding movement along their lengths, radially outer portions received in the second side wall slip windows for movement therethrough between radially retracted and radially extended positions, and tapered ends facing the tapered ends of the first slips;   a biasing structure operative to engage the first and second slips and resiliently bias them toward their retracted positions; and   a releasable setting structure operative to force the first and second slips from their radially retracted positions to their radially extended positions, the releasable setting structure including a tubular wedge member coaxially and slidably circumscribing the inner mandrel between the first and second slips, the wedge member having a tapered solid first end facing the tapered ends of the first slips, and a second end having a circumferentially spaced series of sidewall slots extending axially inwardly therethrough to define a circumferentially spaced series of collet finger portions of the tubular wedge member, the collet fingers having tapered outer ends that face the tapered ends of the second slips,   the inner mandrel, the first and second slips, and the wedge member being relatively movable in axial directions between (1) a set position in which the outer ends of the collet finger portions outwardly overlie and are radially supported by nonpocketed areas of the inner mandrel, with the opposite ends of the wedge member rampingly engaging the tapered ends of the first and second slips, and (2) a release position in which the outer ends of the collet finger portions overlie the second series of inner mandrel pockets and may be radially deflected thereinto in response to an axially directed engagement force between the outer ends of the collet finger portions and the tapered ends of the second slips.   
     
     
       15. The tubular anchor assembly of claim 14 wherein: the inner mandrel has upper and lower ends, and the first slips are positioned axially above the second slips.   
     
     
       16. The tubular anchor assembly of claim 14 wherein: the first and second slips have radially outer sides in which recesses are formed, and   the biasing structure includes: a circumferentially spaced series of arcuate, elongated first spring members disposed between the inner mandrel and the first slip carrier, interdigitated with the first slips, and resiliently biasing the first slips toward their radially retracted positions, the first spring members being concavely curved toward the inner mandrel, having central longitudinal portions secured to the first slip carrier, and outer end portions extending into the recesses of the first slips and slidingly engaging the first slips, and   a circumferentially spaced series of arcuate, elongated second spring members disposed between the inner mandrel and the second slip carrier, interdigitated with the second slips, and resiliently biasing the second slips toward their radially retracted positions, the second spring members being concavely curved toward the inner mandrel, having central longitudinal portions secured to the second slip carrier, and outer end portions extending into the recesses of the second slips and slidingly engaging the second slips.     
     
     
       17. The tubular anchor assembly of claim 14 wherein: the tubular anchor assembly has an end portion adapted for connection to an end portion of an elongated mill guide member.   
     
     
       18. The tubular anchor assembly of claim 14 wherein: the tubular anchor assembly has a lower end portion adapted for connection to an upper end portion of an elongated mill guide member.   
     
     
       19. The tubular anchor assembly of claim 18 wherein: the upper end portion of the elongated mill guide member has an annular configuration with a circumferentially spaced series of axially extending tooth portions formed on its upper end, and   the lower end portion of the anchor assembly includes a circumferentially spaced series of axial notches formed on the lower end of the inner mandrel and adapted to be interlocked with the mill guide member tooth portions, and a tubular coupling member threadable onto the interlocked portions of the inner mandrel and mill guide member.   
     
     
       20. The tubular anchor assembly of claim 14 wherein: the first slips have exterior side surface gripping tooth portions that spiral in a first direction about the longitudinal axis of the inner mandrel, and   the second slips have exterior side surface gripping tooth portions that spiral in a second direction about the longitudinal axis of the inner mandrel, the second direction being opposite from the first direction.